The present invention generally relates to refrigeration systems, and more particularly, to modulate closed condensing loops for use therewith.
In a typical refrigeration system, particularly those found in supermarkets, a plurality of evaporators are used to refrigerate foodstuff in refrigerated display cases. Such systems basically comprise a closed circuit having a compressor stage, a condenser stage, an expansion stage and an evaporator stage. Other stages may be added to the above described basic refrigeration circuit in order to recuperate heat, or to provide refrigeration systems with defrosting loops for high speed defrosting of the evaporators. For instance, U.S. Pat. No. 5,673,567, issued on Oct. 7, 1997 to the present assignee, discloses a refrigeration system with a heat reclaim loop for recuperating heat from hot high pressure refrigerant gas outletting from the compressor stage, rather than evacuating the heat through the condensers, where the heat would be lost to the atmosphere. Thus, the heat reclaim loop is provided in parallel to the condenser stage in order to recuperate heat in heat exchange devices rather than rejecting it to the atmosphere. Preferably, in the cooler seasons, the heat is used for heating the entrance area and other specific colder areas of supermarkets. In the warmer months, the heat may be recuperated for heating water.
U.S. Pat. No. 5,826,433, issued on Oct. 27, 1998 to the present assignee, discloses modification to the above described patent, whereby a modulating valve is provided for efficiently controlling the rate of heat reclaim versus the heat rejection through the condenser stage.
Finally, U.S. Pat. No. 6,089,033, issued on Jul. 18, 2000 to the present assignee discloses a refrigeration system configuration in order to defrost evaporator units at higher speeds.
These refrigeration systems, and generally most refrigeration systems used in supermarkets, have roof top condensers in order to reject heat at the outlet of the compressor stage, whereby the refrigerant is condensed at least partially to a liquid state. Unfortunately, the loops to the roof top condensers extend the piping length of the refrigeration system. Accordingly, the piping networks of refrigeration systems are filled with refrigerant to provide every stage with the necessary conditions for refrigeration. Furthermore, with the advent of heat reclaim loops and high speed defrost cycles, even more refrigerant is used.
Unfortunately, the refrigerants typically used in such refrigeration systems (i.e. refrigerants 404, 408, 507, AZ-20 and the like) are expensive and are often volatile, whereby they may be hazardous to human health and to the environment. The more these refrigerants are used, the higher is the risk of polluting the environment.
It is a feature of the present invention to provide a refrigeration systems having reduced amounts of the above stated refrigerants.
It is a further feature of the present invention to provide a refrigeration system optimizing heat reclaim with respect to compressor operation.
According to the above feature of the present invention, and from a broad aspect thereof, the present invention provides a refrigeration system having a main refrigeration circuit having a condensing stage, wherein a first refrigerant in a high pressure gas state is condensed at least partially to a liquid state. The condensing stage has a pair of stand-alone condensing stage closed loops in heat exchange relation with the main refrigeration circuit. The stand-alone condensing stage closed loops are parallel one to another and each comprise a second refrigerant circulating between at least a heat absorption stage, wherein the second refrigerant absorbs heat from the first refrigerant in the main refrigeration circuit so as to condense the first refrigerant to the liquid state, and a heat release stage, wherein the second refrigerant releases the absorbed heat. The condensing stage has modulating valves for selectively and quantitatively modulating the temperature of said first refrigerant and compressor head pressure.